Telecommunications and data transmission systems have evolved in recent years which are designed to accommodate not only greater numbers of users, but also higher data rates, as a consequence of the use of higher and higher frequencies and huge increases in signaling traffic. Although present day cables and wiring can, theoretically, handle such increased frequencies and traffic volume, the wiring paths themselves become, in effect, antennae which both radiate and receive electromagnetic radiation, thereby creating crosstalk problems. This crosstalk problem is aggravated when station hardware requires multiple wire-pairs. Signal coupling (crosstalk) between different pairs of wires is a source of interference that degrades the capabilities of the apparatus to process incoming signals. This is manifested quantitatively as decreased signal-to-noise ratio and, consequently, increased error rate in the signal processing. As the necessary increases in frequency are implemented, the crosstalk problem becomes of increasingly significant concern.
Various expedients have been used for reducing crosstalk in cables, such as shielding individual pairs, helically winding twisted pairs, or, where possible, increasing the physical separation of one pair from another. However, crosstalk also occurs in station hardware and its connection to the cable or cables. For reasons of economy, convenience, and standardization, it is desirable to extend the utility of the station hardware components, especially plugs and jacks, to higher and higher frequencies or data rates while minimizing any departure from established standard components. Unfortunately, the plugs and jacks that are most commonly used in interconnecting cables and hardware, such as distribution modules, generally include up to eight wires (four pairs) that are necessarily oriented both parallel and close together, a condition that leads to excessive crosstalk, even over short distances, and which is exacerbated as the frequency of the signals or the data rate is increased. Thus, inasmuch as the plugs and jacks generally meet ANSI/EIA/TIA standards for wire and terminal connections, undesired and often unacceptable crosstalk is produced.
There have been numerous attempts to design, within the parameters of standardization, components which reduce crosstalk. In U.S. Pat. No. 5,186,647 of Denkmann et al., there is shown an electrical connector arrangement specifically aimed at reducing crosstalk without drastically altering the general configuration of a standard connector. The connector of that patent comprises a number of input and output terminals interconnected by a pair of lead frames mounted on a dielectric spring block. Each lead frame comprises a plurality of flat, elongated conductors each being terminated by a spring contact at one end and an insulation displacement connector at the other end. In accordance with ANSI/EIA/TIA 568 standard, the terminal assignment for what is designated wire pair I (terminals 4 and 5) is straddled by the terminal assignment for wire pair III (terminals 3 and 6), a condition which produces especially troublesome crosstalk. In order to compensate for, or to diminish, this crosstalk, three of the conductors of one lead frame overlap three of the conductors of the other lead frame within a designated crossover region, thereby inducing compensating crosstalk among specific ones of the conductors occurring in use. Even though such an arrangement has been found to function quite well in reducing crosstalk, it does necessitate some modification of existing hardware, and thus represents an added expense. As a consequence, other solutions to the crosstalk problem have been sought. In U.S. Pat. No. 5,674,093 of Vadeu there is shown an electrical connector arrangement wherein the spring contacts, which normally are parallel to each other, are made non-parallel between their free ends and the major bend characteristic of most connector spring contacts. Because the adjacent contacts are not parallel to each other, the crosstalk inducing capacitance therebetween is reduced, thus producing a reduced crosstalk characteristic. Also, where alternate ones of the contacts have the same shape, there is a capacitive de-coupling effect. Such an arrangement materially reduces crosstalk, but the especially troublesome crosstalk between pairs I and III (as explained hereinafter) is still too close to an undesirable or intolerable amount.
It has been found that the effect of the crosstalk coupling induced by the standard modular plug and jack interface can be reduced to a great extent by the judicious placement of conductors after they exit the modular jack so as to induce crosstalk signals of opposite phase to those which were induced inside the plug and jack. Such a judicious placement of the conductors can be accomplished by having the conductors exit from the modular jack to a printed wiring board, in which case the routing of the wires on the board can be such as to produce a net reduction in crosstalk. The circuit traces that form the pairs of conductors preferably are routed in a pattern that produces crosstalk opposite in polarity to the crosstalk produced in the jack and plug. In U.S. patent application Ser. No. 08/711,699 of Pharney et al., filed Sep. 6, 1996, there is shown and described a crosstalk compensation circuit board member for use with communications systems connector arrays, such as a distribution module. The circuit board member comprises a wiring board on which are printed conductive paths for each of the leads of the several (usually four) pairs in a connector jack, and the board may accommodate several such jacks. The conductive paths are routed in a manner to create facing inductive loops which, for greatest interaction, are substantially mirror images of each other to produce inductive interaction among the different pair combination. The conductive paths can also be routed to incorporate capacitive coupling as well as inductive coupling. Such an arrangement is highly effective in reducing the deleterious effects of crosstalk, however, while it is effective with standard plugs and jacks, it requires a particular, unique, circuit board configuration.
What is needed and is apparently not known in the prior art is an arrangement for achieving a net reduction in crosstalk without the necessity of drastic modification of one or more standardized components, unique circuit board configuration, or crosstalk compensating crossovers of different conductor pairs within one of the components such as the dielectric spring block connector jack.